Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, and various signal processing circuits.
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual images for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The structure of semiconductor material allows the material's electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed operations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each semiconductor die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual semiconductor die from the finished wafer and packaging the die to provide structural support, electrical interconnect, and environmental isolation. The term “semiconductor die” as used herein refers to both the singular and plural form of the words, and accordingly, can refer to both a single semiconductor device and multiple semiconductor devices.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and are produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller semiconductor die size is achieved by improvements in the front-end process resulting in semiconductor die with smaller, higher density active and passive components. Back-end processes result in semiconductor device packages with smaller footprints by improving electrical interconnection and packaging materials. A reduced package profile is of particular importance for packaging in the cellular or smart phone industry.
One approach to achieving the objectives of greater integration and smaller semiconductor devices is to focus on three dimensional (3D) packaging technologies and the electrical interconnection between vertically stacked semiconductor die and devices. In a stacked semiconductor die package, a bottom semiconductor die is mounted to a substrate, a top semiconductor die is mounted over the bottom semiconductor die, and discrete devices are mounted over the substrate adjacent to the stacked semiconductor die. The substrate provides electrical interconnection between the components mounted over the substrate and between the components mounted over the substrate and external devices. However, mounting stacked die and other devices over the substrate increases package profile as the thickness of the substrate increases overall package thickness and mounting discrete devices adjacent to the semiconductor die increases package footprint. Further, when flipchip semiconductor die are stacked, a larger bump is required between the top semiconductor die and substrate, as the bump needs to span the thickness of the bottom semiconductor die. Larger bumps restrict interconnect pitch and reduce the input/output (I/O) count. In addition, larger bumps are susceptible to collapse which can cause electrical short and device defects.